Prehistory of nakedness and clothing
Evolution of hairlessness
The general hairlessness of humans in comparison to related species may be due to loss of functionality in the pseudogene KRTHAP1 (which helps produce keratin) in the human lineage about 240,000 years ago.[1] On an individual basis, mutations in the gene HR can lead to complete hair loss, though this is not typical in humans.[2] Humans may also lose their hair as a result of hormonal imbalance due to drugs or pregnancy.[3]
In order to comprehend why humans have significantly less body hair than other primates, one must understand that mammalian body hair is not merely an aesthetic characteristic; it protects the skin from wounds, bites, heat, cold, and UV radiation.[4] Additionally, it can be used as a communication tool and as a camouflage.[5]
The first member of the genus Homo to be hairless was Homo erectus, originating about 1.6 million years ago.[6] The dissipation of body heat remains the most widely accepted evolutionary explanation for the loss of body hair in early members of the genus Homo, the surviving member of which is modern humans.[7][8][9] Less hair, and an increase in sweat glands, made it easier for their bodies to cool when they moved from living in shady forest to open savanna. This change in environment also resulted in a change in diet, from largely vegetarian to hunting. Pursuing game on the savanna also increased the need for regulation of body heat.[10][11]
Anthropologist and paleo-biologist Nina Jablonski posits that the ability to dissipate excess body heat through eccrine sweating helped make possible the dramatic enlargement of the brain, the most temperature-sensitive human organ.[12] Thus the loss of fur was also a factor in further adaptations, both physical and behavioral, that differentiated humans from other primates. Some of these changes are thought to be the result of sexual selection. By selecting more hairless mates, humans accelerated changes initiated by natural selection. Sexual selection may also account for the remaining human hair in the pubic area and armpits, which are sites for pheromones, while hair on the head continued to provide protection from the sun.[13] Anatomically modern humans, whose traits include hairlessness, evolved 260,000 to 350,000 years ago.[14]
Phenotypic changes
Humans are the only primate species that have undergone significant hair loss and of the approximately 5000 extant species of mammal, only a handful are effectively hairless. This list includes
With the loss of fur, darker, high-melanin skin evolved as a protection from ultraviolet radiation damage.[15] As humans migrated outside of the tropics, varying degrees of depigmentation evolved in order to permit UVB-induced synthesis of previtamin D3.[16][17] The relative lightness of female compared to male skin in a given population may be due to the greater need for women to produce more vitamin D during lactation.[18]
The sweat glands in humans could have evolved to spread from the hands and feet as the body hair changed, or the hair change could have occurred to facilitate sweating. Horses and humans are two of the few animals capable of sweating on most of their body, yet horses are larger and still have fully developed fur. In humans, the skin hairs lie flat in hot conditions, as the arrector pili muscles relax, preventing heat from being trapped by a layer of still air between the hairs, and increasing heat loss by convection.
Sexual selection hypothesis
Another hypothesis for the thick
Water-dwelling hypothesis
The aquatic ape hypothesis (AAH) includes hair loss as one of several characteristics of modern humans that could indicate adaptations to an aquatic environment. Serious consideration may be given by contemporary anthropologists to some hypotheses related to AAH, but hair loss is not one of them.[20]
Parasite hypothesis
A divergent explanation of humans' relative hairlessness holds that
The "ectoparasite" explanation of modern human nakedness is based on the principle that a hairless primate would harbor fewer parasites. When our ancestors adopted group-dwelling social arrangements roughly 1.8 mya, ectoparasite loads increased dramatically. Early humans became the only one of the 193 primate species to have
It was expected that dating the split of the ancestral human louse into two species, the
Fire hypothesis
Another hypothesis is that humans' use of fire caused or initiated the reduction in human hair.[29]
Childrearing hypothesis
Another view is proposed by James Giles, who attempts to explain hairlessness as evolved from the relationship between mother and child, and as a consequence of bipedalism. Giles also connects romantic love to hairlessness.[30][31]
The last common ancestor of humans and chimpanzees was only partially bipedal, often using their front legs for locomotion. Other primate mothers do not need to carry their young because there is fur for them to cling to, but the loss of fur encouraged full bipedalism, allowing the mothers to carry their babies with one or both hands.[32] The combination of hairlessness and upright posture may also explain the enlargement of the female breasts as a sexual signal.[9] Giles' theory is that the loss of fur also promoted mother-child attachment based upon the pleasure of skin-to-skin contact. This may explain the more extensive hairlessness of female humans and infants compared to adult males. Nakedness also affects sexual relationships as well, the duration of human intercourse being many times the duration of any other primates.[24]
Origin of clothing
The current empirical evidence for the origin of clothing is from a 2010 study published in Molecular Biology and Evolution. That study indicates that the habitual wearing of clothing began at some point in time between 83,000 years ago and 170,000 years ago based upon a genetic analysis indicating when clothing lice diverged from their head louse ancestors. This information suggests that the use of clothing likely originated with anatomically modern humans in Africa prior to their migration to colder climates, allowing them to do so.[33]
Some of the technology for what is now called clothing may have originated to make other types of adornment, including
The origin of complex, fitted clothing required the invention of fine stone knives for cutting skins into pieces, and the
The earliest archeological evidence of fabric clothing is inferred from representations in figurines in the southern Levant dated between 11,700 and 10,500 years ago.[42] The surviving examples of woven cloth are linen from Egypt dated 5,000 BCE, although knotted or twisted flax fibers have been found as early as 7000 BCE.[43]
While adults are rarely completely naked in modern societies, covering at least their genitals, adornments and clothing often emphasize, enhance, or otherwise call attention to the sexuality of the body.[44]
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- ^ Couch, Alan (3 February 2016). "Fur or fire: Was the use of fire the initial selection pressure for fur loss in ancestral hominins?". PeerJ Preprints. 4: e1702v1. . Retrieved 10 February 2016.
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